Thermally protective coupling for a light conduit lighting system

ABSTRACT

A light directing, load bearing, thermally protective coupling for connecting a light conduit, such as a light pipe, to a light source includes a body member having a first end connected with the light source and a second end connected with the light pipe. The body member contains a longitudinal channel which extends from the first end to the second end and includes an inner surface defining the channel which directs light from the light source, through the coupling, to the light pipe. To reduce light loss, the inner surface is provided with a highly reflective finish. The coupling is formed of a thermally conductive metal which dissipates heat from the light source and has a length sufficient to produce a temperature drop which allows the light pipe to be connected with the coupling without damaging the light pipe. The first end of the coupling includes a lip portion which is connected with a gasket provided on a light source reflector cone, and the second end of the coupling can include a collar which interlocks with a mating collar provided on an adjacent light pipe.

FIELD OF THE INVENTION

The present invention relates to lighting systems and, moreparticularly, to a thermally protective coupling for connecting a lightconduit, such as a light pipe, to a light source.

BACKGROUND OF THE INVENTION

The illumination of a large area by a central lighting system has longbeen desired because of its many advantages. For example, a centralizedlight source is easier to maintain than many distributed light sources.Heat generated by a centralized light source can be easily vented fromthe lighted areas, whereas heat from distributed light sources is noteasily vented. A light distribution system connected to a centralizedlight source radiates minimal or no heat.

Light pipes or light conduits made of a transparent material havingsubstantially planar inner surfaces and outer surfaces which are “inoctature” have been utilized to transport light, as illustrated in U.S.Pat. No. 4,260,220 to Whitehead. These devices are typically constructedof an optical lighting film made of flexible polymeric sheets of atransparent material having a structured surface on one side and asmooth surface opposite the structured surface. The structured surfaceof the devices preferably includes a linear array of miniaturesubstantially right angle isosceles prisms arranged side-by-side to forma plurality of peaks and grooves. Further, the perpendicular sides ofthe prisms make an angle of approximately 45 degrees with the smoothersurface. This structure of the polymeric sheets, as well as the shape ofthe light conduit, enables light to be constrained to travel through thelight conduit without escaping through its walls if the angle by whichthe light rays deviate from the longitudinal axis of the light conduitdoes not exceed a critical angle. Thus, light entering a light conduitat an angle less than the critical angle is totally internallyreflected.

The critical angle is defined as the arc sine of the ratio of the indexof refraction of the surrounding medium (typically air) to that of thewall material. For example, for a transparent material ofpolymethylmethacrylate having a refractive index of 1.493, all incidentlight rays less than the critical angle of about 27.3 degree, asmeasured along the longitudinal axis of the light conduit, will betotally internally reflected. On the other hand, incident light thatenters the light conduit outside the critical angle will not be totallyinternally reflected.

Alternatively, a light conduit can be constructed using a multi-layeroptical film, such as disclosed in U.S. Pat. No. 5,661,839 (Whitehead).Light conduits have been constructed with various cross-sections, suchas square cross-sections as illustrated in U.S. Pat. No. 4,260,220, andcircular cross-sections, as illustrated in U.S. Pat. No. 4,805,984.

In many applications, it is desirable to allow the light to escape fromthe light conduit in a controlled manner. Many means for facilitatingemission of light from the light conduit have been used in the past,such as disclosed in U.S. Pat. No. 5,363,470 (Wortman). In anotherexample, an extractor such as a diffuse scatterer made of a highlyreflective white polymeric tape such as SCOTCHCAL ELECTROCUT brand film,manufactured by Minnesota Mining and Manufacturing Company, St. Paul,Minnesota, can be placed inside a light conduit to increase the rate ofleakage, or emission, of the light from inside the light conduit. Thediffuse scatterer increases the rate of leakage by “scattering” lightthat hits it into non-total internal reflecting angular regions of thelight conduit, thereby increasing the amount of light in those angleswhich allow light to be emitted from the light conduit. Typically astrip of the highly reflective while polymeric tape is placed over thelength of the light conduit to cause the scattering.

Current light distribution systems utilize segmented light conduitsattached to a light source. The segments of light conduit can be joinedto each other or to the light source by a variety of techniques. TheU.S. Pat. No. 5,475,785 to Johanson, for example, discloses overlappingadjacent ends of the light source and the light conduit to form theconnection. The heat generated by a light source during operation,however, can damage the materials typically used to construct lightconduits. It would therefore be desirable to provide a connectionbetween the light conduit and light source which protects the lightconduit from the intense heat of the light source without interferingwith the operation of the light distribution system.

SUMMARY OF THE INVENTION

The present invention provides a light directing thermally protectivecoupling for connecting a light conduit, such as a light pipe, to alight source. The coupling includes a body member having a first endconnected with the light source and a second end connected with thelight pipe. The body member contains a longitudinal channel whichextends from the first end to the second end and includes an innersurface defining the channel which directs light from the light source,through the coupling, to the light pipe. To reduce light loss, the innersurface is provided with a highly reflective finish. In one embodiment,the body member is formed of a thermally conductive metal which conductsheat away from the light source and dissipates the heat. The body memberhas a length sufficient to produce a temperature drop between the lightsource and the remote end of the coupling so that the light pipe can beconnected with the coupling without having the high temperature of thelight source damage the light pipe. The coupling also provides anincreased surface area which increases convective heat transfer, andfurther provides protection against radiative heat transfer.

In one embodiment, the coupling contains a plurality of radial holeswhich enhance convective heat transfer, and a reflective insert isarranged within the coupling to direct light through the coupling and toprovide protection against radiative heat transfer. The first end of thecoupling includes a lip portion which is connected with a gasketprovided on the light source reflector cone, and the second end of thecoupling can include a collar which interlocks with a mating collarprovided on the adjacent end of an associated light pipe.

In addition to providing thermal protection and efficiently directinglight, the coupling of the present invention is easy to install and cantransmit axial forces, such as those created by thermal expansion andcontraction, between the light source and the light pipe assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be further described with reference to theaccompanying drawings, wherein like reference numerals refer to likeparts in the several views, in which:

FIG. 1 is a perspective view of a lighting system including a thermallyprotective coupling according to the present invention;

FIG. 2 is a cross-sectional view taken along line 2—2 of FIG. 1;

FIG. 3 is a perspective view of a thermally protective coupling;

FIG. 4 is a side view of an alternate embodiment of the invention;

FIG. 5 is a perspective view of an alternate lighting system including athermally protective coupling according to the present invention; arid

FIG. 6 is a cross-sectional view taken along line 6—6 of FIG. 5.

DETAILED DESCRIPTION

Referring now to FIG. 1-3, there is shown a lighting system 2 includinga light source 4, a coupling 26 connected with the light source, a lightpipe assembly 6 connected with the coupling 26, and a mounting assembly8 for hanging the lighting system 2 from a support surface (not shown),such as a ceiling. Additional details of the mounting assembly aredescribed in co-pending U.S. patent application Ser. No. 09/249,364, nowU.S. Pat. No. 6,152,578, which is assigned to the same assignee as thepresent invention and which is hereby incorporated by reference Thelight source is intended to represent a high intensity light source suchas the LIGHTDRIVE 1000™ available from Fusion Lighting, Inc., Rockville,Md. The light source includes a housing 10, and a reflector cone 12containing a light bulb 14. The light pipe assembly, such as the 3MLPS1010 light pipe system available from Minnesota Mining andManufacturing Company, St. Paul, Minn., includes a plurality ofinterconnected light pipes 16. For simplicity, only one such light pipeis shown.

The mounting assembly includes a main housing bracket 18 connected withthe light source housing 10, an elongated light source support rail 20fixedly connected with the housing bracket 18, and a pair of hangerbrackets 22, 24 mounted on the support rail 20. The hanger brackets 22,24 are fixedly connected with the support surface. Each light pipe 16includes a support rail 40 which extends along the length of the lightpipe. A light pipe hanger bracket 41, similar to the light source hangerbrackets 22, 24, is mounted to the support surface and slidably engagesthe light pipe support rail 40, thereby allowing the light pipe 16 andlight pipe support rail 40 to move relative to the support surface inresponse to changes in the overall length of the light pipe assembly 6caused by, for example, thermal expansion and contraction. Additionalhanger brackets can be provided on light pipe support rail 40 forincreased support. A connector or guide clip 42 connects the lightsource support rail 20 with the light pipe support rail 40. The guideclip 42 includes a pair of projections 42 a which engage notches 44, 46contained in the light source support rail 20 and light pipe supportrail 40, respectively, which prevent the support rails from becomingseparated. Thus, during contraction of the light pipe assembly, atensile force is transmitted through the guide clip, and duringexpansion, a compressive force is transmitted through the guide clip.Alternatively, during expansion, the ends of the light source supportrail 20 and the light pipe support rail can abut so that the compressiveforce will be transmitted directly through the support rails 20, 40without going through the guide clip 42.

The coupling 26, which is shown separate from the lighting system inFIG. 3, provides a thermally protective interface between the light pipe16 and the reflector cone 12. A typical light pipe includes a shell andan optical lighting film formed of various materials, such aspolycarbonate and/or acrylic. These materials can be charred, melted, orotherwise damaged by high temperatures. Accordingly, a thermallyprotective interface is necessary to protect the light pipe from thehigh temperatures generated by high intensity light sources, such assulfur plasma lights, which would otherwise damage the light pipe if thelight pipe were connected directly to the reflector cone 12. Thecoupling 26 can be formed of a thermally conductive metal, such asaluminum, so that heat is conducted away from light source 4 andeffectively dissipated. In addition, the high thermal conductivityprovides a temperature drop over the length of the coupling which islarge enough to allow the light pipe 16 to be connected with thecoupling 26 without damaging the light pipe. The length of the couplingcan be adjusted to achieve the desired temperature drop, and thereforeallow light pipes formed of various materials to be connected with thecoupling without damaging the light pipe.

The coupling 26 has a hollow cylindrical shape and includes a first end28 which is connected with the light source 4 and a second end 30 whichis connected with the light pipe 16. More specifically, the couplingincludes a lip portion 26 a which is connected with the reflector cone12, a flared end portion 26 b which is connected with the light pipe 16,and a narrow intermediate portion 26 c having a smaller diameter thanthe flared end portion 26 b extending between the lip portion 26 a andthe flared end portion 26 b. The flared configuration of the coupling isprovided to properly align the reflector cone 12 with the light pipe 16.The coupling can also have a tapered configuration. In addition, theflared end portion 26 b and the intermediate portion 26 c can have thesame diameter depending on the diameter of the reflector cone and thediameter of the light pipe and further depending on how the coupling isconnected with the reflector cone and light pipe. The coupling 26contains a longitudinal internal channel 32 which extends through thecoupling, and includes an inner surface 34 which directs light from thelight source 4 to the light pipe 16. The inner surface 34 can be, forexample, a highly reflective polished metal surface which directs thelight through the coupling. In addition, the polished metal surface caninclude a reflective coating to further increase reflection. To minimizelight loss and thereby optimize performance, the inner surface is madeas highly reflective as possible. A typical highly reflective surfacecan be as much as 96% reflective or greater. While a coupling having alow reflectivity will perform adequately, the highest possiblereflectivity is desired. The highly polished inner surface 34 surfacealso provides thermal protection by dispersing the radiant heat transferfrom the light source 4. However, the coupling will provide thermalprotection even if the inner surface is not highly reflective. Thecoupling 26 also provides an increased surface area for convective heattransfer. Thus, the thermal coupling provides thermal protection byconducting heat from the light source 4, by providing a radiationdispersing barrier which provides thermal protection against radiativeheat transfer, and by increasing the convective heat transfer. Thecoupling is therefore cooled enough to allow the light pipe 16 to beconnected with the reflector cone 12 without damaging the light pipe.While the coupling and its inner surface are shown as having circularcross-sections, other geometric configurations, such as square ortriangular, can be used without significantly affecting the operation ofthe coupling.

FIG. 4 shows a thermally protective coupling 126 including a collar 172which is adapted to connect with a mating collar provided on an adjacentend of the light pipe as described below. The coupling 126 contains aplurality of radially arranged openings 174 which provide the couplingwith enhanced heat dissipation properties. To prevent light fromescaping from the coupling 126, a light directing insert 176 is arrangedconcentrically within the coupling 126. The insert can be formed ofpolished aluminum having a highly reflective mirror like interiorfinish. Alternatively, since the insert 176 provides a certain degree ofthermal protection to the coupling, the coupling 126 can be formed ofother materials, such as polycarbonate.

In addition to providing thermal protection for the light pipe 16, thecoupling 26 is easy to install and forms a strong connection with thereflector cone 12. A coupling gasket 50 connects the coupling 26 withthe reflector cone 12. The coupling gasket 50 includes an annulartransversely extending groove 52 which receives the end of the lightpipe 16 if the coupling 26 is not used and the light pipe 16 isconnected directly with the reflector cone 12. As noted previously,however, the light pipe can be damaged by the heat generated from thelight if the light pipe is connected directly to the reflector cone 12.In addition, such a connection requires an installer to apply caulk tothe joint between the coupling gasket 50 and the light pipe 16 to securethe connection. The coupling gasket 50 also includes an inwardlydirected annular groove 54 which receives the edge of the reflector cone12, the edge of a transparent cover 56 for the reflector cone 12, and alip portion 26 a of the coupling 26. A V-band clamp 58 arranged aroundcoupling gasket 50 is used to tighten the coupling gasket connection.Other known connecting techniques, such as clamps, bolted flanges, orbuckles, can also be used to connect the coupling 26 with the reflectorcone 12.

An annular gasket 60 is provided between the light pipe 16 and thecoupling 26 to produce a tight seal therebetween. In addition, a strap62 extends around the joint formed by the light pipe 16, the annulargasket 60, and the coupling 26 to provide added support for theconnection and to provide a more effective seal. The strap 62 is securedto the outer surface of the guide clip 42. The strap can also befastened to the support rails 20, 40, the light pipe 16, or the coupling26.

FIGS. 5 and 6 show the coupling 126 and insert 176 installed in a lightsystem including an alternate mounting assembly. Additional details ofthis mounting system are also described in pending U.S. patentapplication Ser. No. 09/249,364, now U.S. Pat. No. 6,152,578, which isassigned to the same assignee as the present invention and which ishereby incorporated by reference. The mounting assembly includes a shellor casing 164 which receives the chassis 166 of the light source 104.The chassis 166 contains the reflector cone 112 and the light sourcehousing (not shown). An elongated support rail 120 is formed integrallywith and extends along the top surface of the casing 164.

In contrast to the mounting assembly of FIGS. 1 and 2, the light sourcesupport rail 120 of FIGS. 5 and 6 is not connected with the light pipesupport rail 140. Rather, the entire length of the light source supportrail 120 is contained within the length of the casing 164. Withoutconnecting the support rails 120 and 140, however, tensile andcompression forces are transmitted from the light pipe 116 to thereflector cone 112 through the coupling 126. Since the connectionbetween the light pipe 16 and coupling 26 described in reference toFIGS. 1 and 2 is not suited to transmit tensile forces, FIGS. 5 and 6show an alternate connection between the coupling 126 and light pipe 116which serves to transmit both tensile and compressive forces. Theconnection includes mating interlocking collars 172, 178 on adjacentends of the light pipe 116 and the coupling 126. A suitable connectionis described more fully in pending U.S. patent application Ser. No.09/060,727, now U.S. Pat. No. 6,130,976, which is assigned to the sameassignee as the present invention and which is hereby incorporated byreference. A clamp 180 encloses the collars. Alternatively, the lightpipe 116 can be connected directly to the coupling gasket 150, wherebythe coupling 126 is eliminated.

While several embodiments of the present invention have now beendescribed, it will be apparent to those of ordinary skill in the artthat various changes and modifications may be made without deviatingfrom the inventive concept set forth above. Thus, the scope of thepresent invention should not be limited to the structures described inthis application, but only by the structures described by the languageof the claims and the equivalents of those structures.

What is claimed is:
 1. A light directing, load bearing, thermally protective coupling assembly for connecting a hollow light pipe to a light source, comprising: (a) a coupling formed of a thermally conductive metal and containing a plurality of heat dissipating holes, said coupling having a first end with a lip portion adapted for engagement with a gasket provided on the light source and a second end including a collar adapted for mating engagement with a collar connected with the light pipe, said coupling containing a longitudinal channel extending from said first to said second end, said coupling including an intermediate portion extending from said first end having a first diameter and a flared portion extending from said intermediate portion having a second diameter greater than said first diameter; and (b) a polished reflective sleeve arranged within said coupling channel to direct light from the light source to the light pipe. 